This contract was awarded to undertake a prospective study of plasma levels of testosterone, estradiol, FSH, LH and 20a-dihyfroprogesterone on two occasions prior to vasectomy, at the time of vasectomy and at various times after vasectomy. Subjects (200) were selected from the Vasectomy Clinic at Planned Parenthood of Houston. Post vasectomy blood samples were obtained 1 week, 6 weeks, 3 months, 1 year, and 2 years after sugery. Each determination was performed in duplicate by radioimmunoassay. Seminal fluid smaples were evaluated prior to vasectomy and at 3 months, 1 year, and 2 years after vasectomy.